The present invention relates to an image sensing method, an image sensing apparatus, and an image sensing system and, more particularly, to a method for establishing synchronization between an image sensing unit and a signal processing unit connected with a cable, or the like, in an image sensing system, and an image sensing apparatus and an image sensing system adopting the method.
A variety of image sensing systems, so-called head-detachable cameras, using a solid-state image sensing device, such as a charge-coupled device (CCD), have been proposed. In such systems, an image sensing unit (camera head) and a signal processing unit for processing signals from the image sensing unit and outputting as video signals are separately configured, and connected with a cable, or the like.
Further, an image sensing apparatus using a CCD has been down-sized and down-weighed, and a variety of methods for processing image signals obtained from a CCD in digital form by using high-speed analog-digital (A/D) converter and digital-analog (D/A) converter, realized in the progress of semiconductor manufacturing technique, have been proposed.
Although operability of these head-detachable camera is good, however, a cable for exchanging various kinds of signals, such as an image signal read from a CCD (referred as xe2x80x9cCCD signalxe2x80x9d, hereinafter), a horizontal synchronizing (HD) signal, a vertical synchronizing (VD) signal, and a clock signal (CLK) for establishing synchronization, and other control signals, costs considerable. Further, when the signals CLK and HD, and the CCD signal are transmitted via different signal lines, if the lengths of the signal lines become slightly different from each other by changing the length of the cable, problems in which synchronization is not established and which color signals are reversed may arise because of signal delay in cable. Further, a conventional image sensing system does not have an input unit for inputting synchronizing signal from an external device, it is difficult to establish synchronization between a camera head and a signal processing unit connected to each other.
FIG. 6 is a block diagram illustrating a configuration of a conventional image sensing system. In FIG. 6, reference numeral 200 denotes a camera head, and reference numeral 300 denotes a signal processing unit. In the camera head 200, reference numeral 61 denotes CCD; 62, a sample-and-hold (S/H) circuit for sampling and holding CCD signals; 63, an automatic gain controller (AGC) for controlling a gain for a CCD signal; 64, a timing signal generator (TG) for generating timing signals necessary for the CCD 61, the S/H circuit 62, and so on; and 67, a CPU for controlling each units of a camera head. To the TG 64, a clock signal 2CLK having twice higher frequency than that of a clock signal CLK outputted by the TG 64 is provided. As for the clock signal 2CLK to be provided to the TG 64, in order to increase time precision of various timing signals for operating the CCD 61, one having twice higher frequency than that of the clock signal CLK outputted by the TG 64 is required.
A cable 68 connects the camera head 200 and the signal processing unit 300, and the CCD signals, a clock signal CLK which is synchronized with the CCD signals, and a communication signal RX between the CPU 64 and a CPU 74 are outputted from the camera head 200 to the signal processing unit 300 via the cable 68 which includes a plurality of signal lines. Further, the HD and VD signals for establishing synchronization between the CCD 61 and a digital signal processor (DSP) 70, and a communication signal TX between the CPU 67 and the CPU 74 are outputted from the signal processing unit 300 to the camera head 200 via the cable 68.
The TG 64 establishes horizontal synchronization between the DSP 70 of the signal processing unit 300 and the CCD 61 in accordance with the HD signal. Similarly, the TG 64 establishes vertical synchronization between the DSP 70 and the CCD 61 in accordance with the VD signal. Further, the CPU 67 communicates with the CPU 74 via the communication signals TX and RX, and controls the AGC 63 to adjust the gain for a CCD signal, and also controls an iris diaphragm and zoom lens (not shown) of the camera head 200.
The CCD signals transmitted to the signal processing unit 300 via the cable 68 is converted into digital signals by an analog-digital (A/D) converter 69 in synchronization with the clock signal CLK, applied with digital processes, such as filtering, color separation, Y correction, matrix operation and clipping, which are necessary for color image sensing by the DSP 70. Thereafter, the processed signals are digital-analog converted by a digital-analog (D/A) converter 71, and outputted as signals conforming to NTSC format (video signals).
In the aforesaid example, however, there is a problem in which many signals, such as CCD signals, the HD signal, the VD signal and the clock signal CLK for synchronization, and the communication signals TX and RX, have to be interchanged between the camera head 200 and the signal processing unit 300, and signal lines for transmitting and receiving these signals are necessary, which requires many components for signal transmission and reception, and prevents cost and size of the image sensing system from being reduced.
Further, there is a problem in which, when the length of the cable 68 is changed, because of signal delay, the HD signal, the VD signal and the clock signal CLK may become out of synchronization. Furthermore, when a single CCD each of whose pixels contributes different color component from color components contributed by the neighboring pixels, outputs color CCD signals, if timing of outputting CCD signals and timing of processing the CCD signals by a digital signal processor are out of phase by one pixel period, signals of inverted colors are outputted. For example, a cyan-and-green signal is processed as in the manner for processing a yellow-and-magenta signal, and vice versa.
Further, since a clock generator of the clock signal 2CLK is in the camera head 200 and neither the camera head 200 nor the signal processing unit 300 has an input unit for inputting a synchronizing signal from an external device, thus there is a problem in which synchronization can not be established on the basis of a synchronizing signal from an external device.
The present invention has been made in consideration of the above situation, and has as its first object to provide an image sensing system having a camera head unit and a signal processing unit connected by a less number of signal lines by transmitting a clock signal, a horizontal synchronizing signal, and a CCD signal via a single signal lines in time division, which establishes synchronization between the camera head unit and the signal processing unit when the length of signal lines are changed.
It is the second object of the present invention to make it easy to synchronize a camera head unit and a signal processing unit by synchronizing with a synchronizing signal generated by an external device.
According to the present invention, the foregoing first object is attained by providing a signal processing apparatus which is used by connecting an external device, the apparatus comprising: transmission means for transmitting reference signals to the external device; control means for controlling the external device so as to output a predetermined signal; reception means for receiving the predetermined signal; and phase shifting means for establishing synchronization with the external device by shifting phases of the reference signals on the basis of the predetermined signal received by the reception means.
According to the present invention, the predetermined signal is preferably selected from plural kinds of signals, and transmitted via a single signal line.
Further, the first object is also attained by providing an image sensing apparatus which is used by connecting an external device, comprising: first input means for inputting reference signals from the external device; second input means for inputting a control signal from the external device; and selection means for selecting a predetermined signal, generated on the basis of the reference signals inputted by the first input means, on the basis of the control signal inputted by the second input means and outputting the selected signal.
Further, the first object is also attained by providing an image sensing system having an image sensing apparatus and a signal processing apparatus comprising: communication means for transmitting reference signals from the signal processing apparatus to the image sensing apparatus; control means for controlling the image sensing apparatus so as to output a predetermined signal generated on the basis of the reference signal; selection means for selecting the predetermined signal under control of the control means; and phase shifting means for synchronizing between the signal processing apparatus and the image sensing apparatus by shifting phases of the reference signals on the basis of the predetermined signal selected by the selection means.
According to the present invention, the selection means preferably selects the predetermined signal out of plural kinds of signals and outputs the selected signal to the phase shifting means via a single signal line.
According to the present invention, the foregoing second object is attained by further providing input means for inputting a synchronizing signal from an external device in addition to the above signal processing apparatus, wherein the reference signals are based on the synchronizing signal inputted by the input means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.